Explore the vast range of titles available.

Biological soil crusts (BSCs) cover extensive portions of the earth’s deserts. In order to survive desiccation cycles and utilize short periods of activity during infrequent precipitation, crust microorganisms must rely on the unique capabilities of vegetative cells to enter a dormant state and be poised for rapid resuscitation upon wetting. To elucidate the key events involved in the exit from dormancy, we performed a wetting experiment of a BSC and followed the response of the dominant cyanobacterium, Microcoleus vaginatus, in situ using a whole-genome transcriptional time course that included two diel cycles. Immediate, but transient, induction of DNA repair and regulatory genes signaled the hydration event. Recovery of photosynthesis occurred within 1 h, accompanied by upregulation of anabolic pathways. Onset of desiccation was characterized by the induction of genes for oxidative and photo-oxidative stress responses, osmotic stress response and the synthesis of C and N storage polymers. Early expression of genes for the production of exopolysaccharides, additional storage molecules and genes for membrane unsaturation occurred before drying and hints at preparedness for desiccation. We also observed signatures of preparation for future precipitation, notably the expression of genes for anaplerotic reactions in drying crusts, and the stable maintenance of mRNA through dormancy. These data shed light on possible synchronization between this cyanobacterium and its environment, and provides key mechanistic insights into its metabolism in situ that may be used to predict its response to climate, and or, land-use driven perturbations.

The carbon dioxide (CO₂)-concentrating mechanism of cyanobacteria is characterized by the occurrence of Rubisco-containing microcompartments called carboxysomes within cells. The encapsulation of Rubisco allows for high-CO₂ concentrations at the site of fixation, providing an advantage in low-CO₂ environments. Cyanobacteria with Form-IA Rubisco contain α-carboxysomes, and cyanobacteria with Form-IB Rubisco contain β-carboxysomes. The two carboxysome types have arisen through convergent evolution, and α-cyanobacteria and β-cyanobacteria occupy different ecological niches. Here, we present, to our knowledge, the first direct comparison of the carboxysome function from α-cyanobacteria (Cyanobium spp. PCC7001) and β-cyanobacteria (Synechococcus spp. PCC7942) with similar inorganic carbon (Ci; as CO₂ and HCO₃⁻) transporter systems. Despite evolutionary and structural differences between α-carboxysomes and β-carboxysomes, we found that the two strains are remarkably similar in many physiological parameters, particularly the response of photosynthesis to light and external Ci and their modulation of internal ribulose-1,5-bisphosphate, phosphoglycerate, and Ci pools when grown under comparable conditions. In addition, the different Rubisco forms present in each carboxysome had almost identical kinetic parameters. The conclusions indicate that the possession of different carboxysome types does not significantly influence the physiological function of these species and that similar carboxysome function may be possessed by each carboxysome type. Interestingly, both carboxysome types showed a response to cytosolic Ci, which is of higher affinity than predicted by current models, being saturated by 5 to 15 mm Ci. This finding has bearing on the viability of transplanting functional carboxysomes into the C₃ chloroplast.

Arsenic (As) is a pervasive and ubiquitous environmental toxin that has created worldwide human health problems. However, there are few studies about how organisms detoxify As. Cyanobacteria are capable of both photolithotrophic growth in the light and heterotrophic growth in the dark and are ubiquitous in soils, aquatic systems, and wetlands. In this study, we investigated As biotransformation in three cyanobacterial species (Microcystis sp. PCC7806, Nostoc sp. PCC7120, and Synechocystis sp. PCC6803). Each accumulated large amounts of As, up to 0.39 g kg⁻¹ dry weight, 0.45 g kgɻ¹; dry weight, and 0.38 g kg⁻¹ dry weight when treated with 100 μм sodium arsenite for 14 d, respectively. Inorganic arsenate and arsenite were the predominant species, with arsenate making up >80% of total As; methylated arsenicale were detected following exposure to higher As concentrations. When treated with arsenate for 6 weeks, cells of each cyanobacterium produced volatile arsenicals. The genes encoding the As(III) S-adenosylmethionine methyltransferase (ArsM) were cloned from these three cyanobacteria. When expressed in an As-hypersensitive strain of Escherichia coli, each conferred resistance to arsenite. Two of the ArsM homologs (SsArsM from Synechocystis sp. PCC6803 and NsArsM from Nostoc sp. PCC7120) were purified and were shown to methylate arsenite in vitro with trimethylarsine as the end product. Given that ArsM homologs are widespread in cyanobacteria, we propose that they play an important role in As biogeochemistry.

Lichens are symbiotic associations between fungi and photosynthetic algae or cyanobacteria. Microcystins are potent toxins that are responsible for the poisoning of both humans and animals. These toxins are mainly associated with aquatic cyanobacterial blooms, but here we show that the cyanobacterial symbionts of terrestrial lichens from all over the world commonly produce microcystins. We screened 803 lichen specimens from five different continents for cyanobacterial toxins by amplifying a part of the gene cluster encoding the enzyme complex responsible for microcystin production and detecting toxins directly from lichen thalli. We found either the biosynthetic genes for making microcystins or the toxin itself in 12% of all analyzed lichen specimens. A plethora of different microcystins was found with over 50 chemical variants, and many of the variants detected have only rarely been reported from free-living cyanobacteria. In addition, high amounts of nodularin, up to 60 μg g–1, were detected from some lichen thalli. This microcystin analog and potent hepatotoxin has previously been known only from the aquatic bloom-forming genus NODULARIA: Our results demonstrate that the production of cyanobacterial hepatotoxins in lichen symbiosis is a global phenomenon and occurs in many different lichen lineages. The very high genetic diversity of the mcyE gene and the chemical diversity of microcystins suggest that lichen symbioses may have been an important environment for diversification of these cyanobacteria.

Biological nitrogen fixation (BNF) performed by moss-associated cyanobacteria is one of the main sources of new nitrogen (N) input in pristine, high-latitude ecosystems. Yet, the nutrients that limit BNF remain elusive. Here, we tested whether this important ecosystem function is limited by the availability of molybdenum (Mo), phosphorus (P), or both. BNF in dominant mosses was measured with the acetylene reduction assay (ARA) at different time intervals following Mo and P additions, in both laboratory microcosms with mosses from a boreal spruce forest and field plots in subarctic tundra. We further used a 15N2 tracer technique to assess the ARA to N2 fixation conversion ratios at our subarctic site. BNF was up to four-fold higher shortly after the addition of Mo, in both the laboratory and field experiments. A similar positive response to Mo was found in moss colonizing cyanobacterial biomass. As the growing season progressed, nitrogenase activity became progressively more P limited. The ARA: 15N2 ratios increased with increasing Mo additions. These findings show that N2 fixation activity as well as cyanobacterial biomass in dominant feather mosses from boreal forests and subarctic tundra are limited by Mo availability.

Freshwater cyanobacterial harmful algal blooms (cyanoHABs), often dominated by Aphanizomenon , Dolichospermum , and Microcystis, are intensifying in eutrophic watersheds globally. A potential control on bacterioplankton dynamics in these systems is the availability of the essential metabolic cofactor thiamin (vitamin B 1 ) and presence of the allelopathic thiamin antagonist bacimethrin, which causes competitive inhibition of thiamin-requiring enzymes. We examined dissolved concentrations of thiamin chemical congeners and bacimethrin, 16S amplicon-based microbiome compositions, prokaryotic mRNA-based metatranscriptomes, and reference genomes in hypereutrophic Upper Klamath Basin before and during seasonal cyanoHABs. Our objective was to connect bacterioplankton community compositions and gene expression patterns with thiamin congener and bacimethrin availability under different cyanoHAB conditions. Bacimethrin was present in all samples at similar concentrations to the thiamin precursor, HMP, suggesting that similar mechanisms influence the availability of both compounds. Additionally, bacimethrin concentrations were positively correlated with cyanoHAB species abundance (cells mL -1 ) and the expression of microbial thiamin biosynthesis genes. Samples with high cyanoHAB abundance also displayed elevated transcription of genes in key biochemical pathways such as the pentose phosphate pathway, photosynthesis, and glycogen biosynthesis. Bacterioplankton such as Limnohabitans spp. that are unable to synthesize thiamin, and are thus vulnerable to bacimethrin allelopathy, showed reduced gene expression when cyanoHAB abundance was high. Reference genomes of cyanoHAB and many picocyanobacteria strains contained complete thiamin biosynthesis gene pathways, implicating these taxa as major thiamin sources. These results suggest that bacimethrin provides a competitive advantage to bacterioplankton that do not require exogenous thiamin by eliminating the risk of bacimethrin uptake with thiamin transporters, potentially facilitating cyanoHAB dominance in Upper Klamath Basin and broader eutrophic watersheds.

Banded iron formations (BIF) were deposited abundantly between 2.7-2.4 Ga from iron- and silica-rich oceans, with cyanobacterial oxygen (O 2 ) as a possible oxidant for Fe(II) (aq) oxidation and Fe(III) oxyhydroxide precipitation. However, toxic reactive oxygen species (ROS) from Fe(II)/O 2 interactions might have inhibited cyanobacterial growth, contributing to the delay between cyanobacterial evolution (>3.0 Ga) and the Great Oxidation Event (2.5 Ga). Here, we explored the impact of Fe(II) (aq) and SiO 2(aq) on Synechococcus sp . PCC 7002. High Fe(II) (aq) ( > 500 µM) increased ROS formation, but elevated SiO 2(aq) (2200 µM) suppressed ROS formation, promoting growth and O 2 production. Diel light cycles further reduced ROS formation compared to continuous illumination. Modelling O 2 distribution based on experimental rates revealed oxygenated surface waters at relevant upwelling rates. Together, our results indicate that high SiO 2(aq) and day-night-light cycles in Archean oceans mitigated ROS stress, enabling cyanobacterial proliferation and enhancing their role in Earth’s oxygenation and BIF deposition. This study shows O 2 -producing cyanobacteria likely prospered in silica- and iron-rich ancient oceans prior to the emergence of free O 2 . Silica and day-night light cycles helped the microbes to overcome toxicity effects caused by oxygen radicals.

Three strains of filamentous Cyanobacteria were used to study their growth and utilization of organophosphorus pesticide malathion. A sharp decrease in the growth of the algal strains was observed by increasing the concentration of malathion. Amongst them Nostoc muscorum tolerated different concentrations and was recorded as the highest efficient strain for biodegradation (91%) of this compound. Moreover, carbohydrate and protein content of their cells overtopped the other strains especially at higher concentrations. The algal strains were further subjected to grow under P-limitation in absence and presence of malathion. Although, the algal growth under P-limitation recorded a very poor level, a massive enhanced growth and phosphorous content of cells were obtained when the P-limited medium was amended with malathion. This study clarified that N. muscorum with its capability to utilize malathion as a sole phosphorous source is considered as an inexpensive and efficient biotechnology for remediation of organophosphorus pesticide from contaminated wastewater.

Glyphosate-based herbicides are among the most widely used agricultural chemicals globally, and their widespread application presents risks to environmental health and aquatic ecosystems. Continuous glyphosate inputs disrupt phytoplankton communities, potentially triggering harmful algal blooms. This study examines the proliferation of microalgal species exposed to low glyphosate concentrations (0.05 mg/L) and various phosphorus sources, with a particular focus on C-P and C-O-P bond phosphonates, which have been insufficiently studied in previous research. We hypothesized that cyanobacteria might exhibit a competitive growth advantage over other algal species when exposed to C-P bond glyphosate, especially under phosphorus-limited conditions. In monoculture experiments, Microcystis aeruginosa and Peridinium umbonatum var. inaequale significantly increased their biomass when cultured with C-P bond phosphonates, whereas Scenedesmus bijuga failed to thrive under similar conditions. Peridinium umbonatum var. inaequale also displayed increased soluble protein content in response to glyphosate stress, indicating an adaptive stress response. In co-culture experiments, M. aeruginosa demonstrated greater tolerance to glyphosate than P. umbonatum var . inaequale , though biomass increases were not significantly correlated with soluble protein or APA. Sediment–water interface experiments revealed that glyphosate exposure significantly promoted cyanobacterial biomass, which was approximately five times greater than that of the inorganic phosphorus group. Notably, when cyanobacterial biomass exceeded 20% of the total, Cyanophyta replaced Chlorophyta as the dominant group, suggesting a potential competitive advantage under low-dose glyphosate exposure. These findings highlight that glyphosate may promote cyanobacterial dominance by altering phytoplankton community composition, potentially contributing to the increased frequency of harmful algal blooms in nutrient-limited aquatic environments.

Recent studies on the diazotrophic cyanobacterium Trichodesmium erythraeum (IMS101) showed that increasing CO₂ partial pressure (pCO₂) enhances N₂ fixation and growth. Significant uncertainties remain as to the degree of the sensitivity to pCO₂, its modification by other environmental factors, and underlying processes causing these responses. To address these questions, we examined the responses of Trichodesmium IMS101 grown under a matrix of low and high levels of pCO₂ (150 and 900 μatm) and irradiance (50 and 200 μmol photons m⁻² s⁻¹). Growth rates as well as cellular carbon and nitrogen contents increased with increasing pCO₂ and light levels in the cultures. The pCO₂-dependent stimulation in organic carbon and nitrogen production was highest under low light. High pCO₂ stimulated rates of N₂ fixation and prolonged the duration, while high light affected maximum rates only. Gross photosynthesis increased with light but did not change with pCO₂. HCO₃⁻ was identified as the predominant carbon source taken up in all treatments. Inorganic carbon uptake increased with light, but only gross CO₂ uptake was enhanced under high pCO₂. A comparison between carbon fluxes in vivo and those derived from ¹³C fractionation indicates high internal carbon cycling, especially in the low-pCO₂ treatment under high light. Light-dependent oxygen uptake was only detected under low pCO₂ combined with high light or when low-light-acclimated cells were exposed to high light, indicating that the Mehler reaction functions also as a photoprotective mechanism in TRICHODESMIUM: Our data confirm the pronounced pCO₂ effect on N₂ fixation and growth in Trichodesmium and further show a strong modulation of these effects by light intensity. We attribute these responses to changes in the allocation of photosynthetic energy between carbon acquisition and the assimilation of carbon and nitrogen under elevated pCO₂. These findings are supported by a complementary study looking at photosynthetic fluorescence parameters of photosystem II, photosynthetic unit stoichiometry (photosystem I:photosystem II), and pool sizes of key proteins in carbon and nitrogen acquisition.